United States citizens do not need a U.S. visa or passport for travel to Colorado.
If you are not a U.S. citizen, you may need a visa for entry into the U.S.
Once you register for the conference, you can download a letter indicating that you will be attending the conference.
For additional information regarding visas and/or passports, please visit http://travel.state.gov/
This website will be updated if more information becomes available.